Icings were investigated near the Tibbitt to Contwoyto Winter Road (TCWR) to examine the relation of overflow timing to air and ground temperature, rainfall, snow accumulation, and the winter road. Icings developed before the end of freezeback by intermittent overflow of water from upstream lakes. Open-system freezing in saturated peat caused build-up of hydraulic pressure, leading to overflow. The active layer remained hydrologically active after the overflow period but hydraulic pressures, possibly related to the upstream lake, were insufficient to cause further icings. The duration of the overflow period and spatial extent were positively related to autumn rainfall. In addition, above average early winter air temperature and average early winter snowfall were important factors contributing to overflows at several portages noted in the TCWR maintenance records. Development of icings in the Canadian Shield threshold-mediated hydrological regime is dependent on basin catchment area and antecedent conditions.